Drugs affecting platelet function tests. Their effects on haemostasis and surgical bleeding

This review has attempted to discuss some of the problems related to the potential hemorrhagic effects of drugs inhibiting platelet function. Many compounds are inhibitory in vitro, but only a few are suitable for administration to man. Among the latter, aspirin is certainly the drug most extensively investigated: it prolongs bleeding time and carries some haemorrhagic risk. Local erosive factors are mainly involved in the pathogenesis of aspirin induced gastrointestinal bleeding. However, the possible contributing role of the haemostatic defect induced by aspirin has not been definitely ruled out. No evidence exists at present that other drugs such as dipyridamole and congeners, dextrans, sulfinpyrazone, hydroxychloroquine and indomethacin consistently affect bleeding time and/or impair haemostasis. However, lack of hemorrhagic risk associated with administration of these drugs will only be established by carefully conducted clinical trials. Some of the problems which should be considered when planning such trials are: the disposition of the drug studied (a lack of effect could be simply due to too low an active concentration of the drug in the blood) and the need for an objective and quantitative measurement of bleeding, particularly in surgical patients (the widespread criterion of 'clinical impression' when evaluating hemorrhage must be avoided). Finally, both obstetricians and their patients should be strongly warned about the potential though unproven hemorrhagic risk for newborn infants derived from the maternal ingestion prior to delivery of drugs affecting platelet function.